When choosing a prepaid plan for Russia, be aware that every major Russian city is on a separate mobile network, so once you leave the city where you have purchased your SIM card, you go onto roaming tariffs that can get very expensive. If you’re going to stay in one city, just buy any cheap SIM with data and you’re set. If you’re planning to travel across Russia – the better solution would be to get a plan that provides cheap inter-network roaming from the start. Another option is to actually buy a separate SIM for every new city you plan to spend an extended period of time in.
When buying a SIM card in Russia you will most likely be asked to show your passport & registration.